Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburetors because they give better control of the delivery of fuel and enable the engine to meet emission legislation targets as well as improving overall efficiency.
It is important that the fuel injection system delivers an appropriate amount of fuel at an appropriate time. Inappropriate delivery of the fuel may lead to a reduction in the output power of the engine and a wastage of fuel.
Whilst the sophisticated and highly developed fuel injection systems currently available (as described above) are ideal for use in internal combustion engines in automobiles, there are many other applications for internal combustion engines where such a level of sophistication is not appropriate and too costly. For instance, small single cylinder engines as used for a variety of engine powered gardening devices (such as lawn mowers, hedge trimmers, chain saws, rotovators, lawn aerators, scarifiers and shredders), small generators, mopeds, scooters, etc. are built to very tight cost targets and therefore cannot afford the cost of a sophisticated fuel injection system. To date, such small engines have used traditional cheaper carburetor technology. However, small engines of this type will soon face the same kind of exhaust gas emission legislation as automobile engines and so must be modified to meet the emission targets. Therefore, a cheap and simple system of fuel injection is required for such small engines.
In GB 2425188 the applicant described a fuel injection unit suitable for a small engine. The injector described injects in each operation a set amount of fuel into the charge air; the controller of the unit decided in each engine cycle how much fuel was needed and then operated the injector a number of times to come closest to the ideal amount of fuel. Since the amount of fuel can only be controlled in steps equivalent to the volume dispensed by the injector, the control was quite coarse. The engine could be over-fuelled or under-fuelled.